JP2010520497A - Photonic crystal fiber and method of manufacturing the same - Google Patents

Abstract

A photonic crystal fiber comprising a plurality of extruded non-circular canes, each of the extruded non-circular canes comprising at least one hole. A method of manufacturing a photonic crystal fiber, a step of thermoforming a glass material into a glass tube having a non-circular outer cross section, a step of drawing a glass tube to obtain a plurality of canes, a laminate of canes and a preform Generating a structure, and drawing a preform structure to obtain a photonic crystal fiber.

Description

Explanation of related applications

  This application is incorporated by reference and is incorporated herein by reference in its entirety, US Provisional Patent Application No. 60 / 903,901, filed February 28, 2007, entitled “Photonic Crystal Fiber and It Claims the benefit of "how to manufacture".

  The present invention relates to a photonic crystal fiber and a manufacturing method thereof.

  Conventional optical waveguide fibers exhibit a balance between optical loss, nonlinearity, group velocity, dispersion, and polarization effects. However, photonic crystal fibers (including photonic bandgap fibers, etc.) have become increasingly popular in recent years due to effective techniques to improve nonlinear optical interactions between light pulses and their bulk components. It has spread. Photonic crystal fibers find use in fiber optic communications, fiber lasers, nonlinear devices, high power transmission, high sensitivity gas sensors, and other areas.

  Current photonic crystal fiber manufacturing processes include stack-stretch techniques for forming microstructured arrays. In particular, in the process of lamination-stretching, a large number of glass capillaries are arranged in a grid array in the outer support tube in order to generate a desired macroscopic cross-sectional shape. This array is then drawn and assembled into a fiber. The process of the lamination-stretching method is a manual process, so the process is relatively slow and there is a problem that one preform structure and another are not consistent. Furthermore, due to process inconsistencies, the circularly formed capillaries often undergo misalignment during melting and / or drawing, resulting in voids and defects in the fiber. Such unintentional defects significantly increase the optical loss in the photonic crystal fiber.

  In addition to the problems associated with consistency and defects, it is very difficult to change the shape of the capillary or preform structure in conventional processes. For example, most photonic crystal fibers are drawn from circular fiber preforms, but recently hexagonal studies have been conducted. The conventional manufacturing process of the hexagonal preform includes a process of preparing a tube by CVD and then polishing the outer diameter of the tube to generate a hexagonal shape. This polished hexagonal tube can be predrawn into capillaries, where each capillary is then laminated into a macroscopic array and drawn under vacuum. Not only is it time consuming and expensive to assemble such a hexagonal tube to assemble the preform structure, but also unintended voids in the fiber if the capillary is kinked or moved during the assembly process. There is also a problem that is generated. In this case as well, light loss increases due to unintended voids and defects.

  Therefore, there is a need for a high quality photonic crystal fiber having a unique geometric shape that has few defects and can be produced with good reproducibility.

  The present invention is intended to address and eliminate problems and shortcomings, or to improve upon conventional photonic crystal fibers and methods of manufacturing the same.

  In order to achieve this, an embodiment of the present invention is a method of manufacturing a photonic crystal fiber, the method comprising thermoforming glass material into a glass tube having a non-circular outer cross section, drawing the glass tube. A step of obtaining a plurality of canes, a step of laminating the canes to form a preform structure, and a step of drawing the preform structure to obtain a photonic crystal fiber. Including a method of manufacturing.

To further achieve the above, an embodiment of the present invention is a method of producing a photonic crystal fiber, expressed in terms of weight percent on the oxide basis, 55% to 75% of SiO 2, _5% A glass tube is obtained by extruding a precursor glass material having a composition of 10% Na ₂ O, 20% to 35% B ₂ O ₃ , and 0% to 5% Al ₂ O _3. A tube having a plurality of channels extending along the axis of the tube, a step of eluting the glass tube to obtain a porous glass tube containing at least 90% silica by weight, forming a densified glass Heating the porous glass tube so that the pores in the glass tube collapse to obtain a densified glass tube, drawing the densified glass tube to obtain a plurality of canes, Forming a cane laminate Step each Kane touches the adjacent Kane directly in the lamination members, and, by drawing the laminated member, comprising the method of manufacturing photonic crystal fiber, characterized in that it comprises a step, to obtain a photonic crystal fiber.

  In order to further achieve the above, an embodiment of the present invention is a photonic crystal fiber preform structure comprising a plurality of extruded non-circular canes, each extruded non-circular cane, A photonic crystal fiber preform structure comprising at least one channel extending along the cane axis is included.

  The specification concludes with claims that particularly point out and distinctly claim the invention, which will be better understood from the following description, illustrated in conjunction with the accompanying drawings.

A bottom view showing an exemplary mold for manufacturing an exemplary tube used in a photonic crystal fiber according to the present invention. Schematic showing a typical manufacturing process of a photonic crystal fiber according to the present invention. Schematic showing a typical manufacturing process of a photonic crystal fiber according to the present invention. Schematic showing a typical manufacturing process of a photonic crystal fiber according to the present invention. Image of another exemplary tube manufactured according to an exemplary embodiment of the present invention. Image of another exemplary tube manufactured according to an exemplary embodiment of the present invention. Image of another exemplary tube manufactured according to an exemplary embodiment of the present invention. Schematic showing another representative manufacturing process of a photonic crystal fiber according to the present invention. Schematic showing another representative manufacturing process of a photonic crystal fiber according to the present invention. Schematic showing another representative manufacturing process of a photonic crystal fiber according to the present invention. Schematic showing another representative manufacturing process of a photonic crystal fiber according to the present invention. Schematic showing another representative manufacturing process of a photonic crystal fiber according to the present invention.

  The embodiments illustrated in the drawings are actual examples and are not intended to limit the invention as defined by the claims. Furthermore, the individual features of the drawings and the present invention will become more fully apparent and understood in view of the detailed description.

  Unless otherwise indicated, all numbers, such as weight percentages, dimensions, and specific physical property values of components used in the specification and claims, are qualified in all cases by the term “about”. I want you to understand. It should also be understood that the exact numerical values used in the specification and claims constitute additional embodiments of the invention. So far, efforts have been made to ensure the accuracy of the numerical values disclosed in the examples. However, any measured value may inherently contain some error due to the standard deviation found in each measurement technique.

  The singular forms used in the description and claims of the present invention mean “at least one” and should not be limited to “one and only one” unless explicitly contradicted. Thus, for example, reference to “a cane” includes embodiments having more than one cane, unless the context clearly indicates otherwise. As used herein, “wt%” or “weight percent” or “percent by weight” of a component is based on the total weight of the composition or product in which the component is included, unless otherwise stated. It is. All percentages in this specification are by weight unless otherwise specified.

  As described in more detail herein, the inventor has developed a process for thermoforming or extruding a porous glass tube having a non-circular outer cross section. The formed non-circular tubes can be drawn into smaller diameter tubes and laminated together to create a preform structure. The outer diameter of each tube can also be shaped to match the geometry of the other tubes in order to consistently align and laminate the tubes in the preform structure array. The resulting product can be drawn into a cane (if desired) and coated with an outer tube to draw into a photonic crystal fiber. Photonic crystal fibers manufactured by the processes described herein have unique geometric and transmission characteristics compared to conventional photonic crystal fibers.

  As used herein, the term “photonic crystal fiber” includes photonic crystal fibers, photonic band gap fibers (photonic crystal fibers that confine light by the band gap effect), holey fibers (having holes in the cross section). Photonic crystal fibers), hole-added fibers (photonic crystal fibers that guide light through a conventional high refractive index core modified by the presence of holes), and / or Bragg fibers (multilayer dielectric or metal It will be understood that a photonic band gap fiber formed by concentric rings of films is included.

  In one embodiment, the glass material used in the process of the present invention may be selected from a glass group having a high silica content. In general, such glass-related properties are considered desirable in geometrically complex structures. For example, a glass precursor with a high silica content usually has a softening temperature of around 1500 ° C. or higher, a low thermal expansion and a high UV transmission. In one embodiment, the glass precursor / material may also include a VYCOR® product precursor from Corning, Corning, NY. Generally, Vycor® begins as an alkali borosilicate glass and is subjected to a processing step that converts the alkali borosilicate glass to at least 90% (eg, about 95-96%) silica structure. This about 95-96% silica structure can be a porous or tempered glass body.

Vycor® products and glass precursors thereof are described in Corning US Pat. No. 2,106,744 (the '744 patent), all of which are incorporated herein by reference. It is. As disclosed therein, the glass composition in a region of the ternary system (R ₂ O—B ₂ O ₃ —SiO ₂ ) is separated into two phases by appropriate heat treatment. One of the phases is very rich in silica, whereas the other phase is very rich in alkali and boron oxide. The '744 patent discloses a precursor composition of 75% SiO ₂ , 5% Na ₂ O, and 20% B ₂ O ₃ . However, other precursor compositions used in the methods described herein include, for example, 60.82% SiO ₂ , 7.5% Na ₂ O, 28.7% B ₂ O ₃ , 2. A composition of 83% Al ₂ O ₃ and 0.15% Cl, the softening temperature of such a composition is around 670 ° C., and the thermal expansion coefficient is around 52.5 × 10 ⁻⁷ / K. is there. Of course, (weight percent) 55-75% before and after the _SiO 2, 5 to 10% of _Na 2 O, 20 to 35% of _B 2 _O 3, _0~5% of _Al 2 _O 3, 0 to It should be understood that any other silica glass composition having a composition range of 0.5% Cl is contemplated for use in the method of the present invention.

  While high silica glasses as described herein and / or glasses with relatively low softening temperatures (eg, softened glass) are considered ideal for use in the process according to the present invention, It is to be understood that the present invention is not so limited and that various glasses can be used to obtain the high quality photonic crystal fibers described herein.

  Exemplary process steps for manufacturing photonic crystal fibers are schematically illustrated in FIGS. 1 and 2A-2C. In one embodiment, the mold 20 (the bottom view is shown in FIG. 1) has a hexagonal shape (eg, the periphery of the mold has six sides 22) and has an array of 37 pins 24. Can be included. This hexagonal outer periphery (for example, the outer diameter of the molded shape 26) is an example of a non-circular mold configured to produce a non-circular tube. However, it should be understood that the mold 20 can have any non-circular perimeter that shapes the shape. As used herein, “non-circular” can include triangles, quadrilaterals, pentagons, polygons, parallelograms and trapezoids, or any asymmetric shape, to name a few examples. As described below, the ability to heat or extrude the tube into the desired shape allows the tube to be laminated in a manner that improves manufacturing efficiency and the resulting fiber properties while minimizing defects. It can be suppressed.

  The mold 20 of FIG. 1 is illustrated as having 37 pins 24. The number 37 is considered to be the most effective number for forming a matching number of channels (for example, reference numeral 34 in FIG. 2A) from the viewpoint of space utilization of the hexagonal structure. However, in other embodiments, the hexagonal mold has one, seven, nineteen, thirty-seven, fifty-five, seventy-seven to form a matching number of channels 34 along the axis of tube 30. And so on (any number considering hexagonal symmetry). As shown, the spatial periodicity of the channels in the tube 30 and the multiple canes 40 (e.g., the distance between the closest channels is the same, and all channels are essentially the same except those in the vicinity) With the number of adjacent channels) is basically the same. Furthermore, the spatial periodicity in the laminated member 50 is basically the same as that in each individual cane.

  The number of pins in other non-circular molds may vary from application to application and depending on the desired perimeter symmetry of the tube. However, it is believed that the tunneling loss decreases as the number of channels in the manufactured tube 30 increases. Further, if short wavelength applications are desired, the number of channels may be increased to meet the demand for narrow pitch. Further, the pin 24 of the mold 20 of FIG. 1 is illustrated with a circular shape (and consequently the same as the channel 34 of the tube 30), but as with the overall shape inside the mold 20, the pin 24 (and the result) In particular, it should be understood that the shape of channel 34) can include any shape, such as a triangle, square, pentagon, polygon, parallelogram, or trapezoid, to name a few. As will be described further below, not all pins / channels need be the same size as other pins / channels, such as when an intentional defect is desired. For example, as illustrated in FIG. 1, the pins 24 at each point of the hexagon may be larger than the peripheral pins (eg, the outer corners may be distorted during extrusion). To improve the extruded channel geometry).

  In particular, through the use of the glass described and intended herein, the glass tube is extruded to have any shape (in terms of both outer / outer diameter and hole shape) that would improve the production of the photonic crystal fiber. In contrast, the glass capillaries are limited to a circular shape in the manufacturing and lamination in the conventional process. For example, referring to FIGS. 3A-3C, images of a glass tube 130 manufactured in accordance with an exemplary embodiment of the present invention are shown. In FIG. 3A, the glass tube 130 has a hexagonal outer cross section / perimeter / outer diameter 132 and a single hexagonal hole 134. Thereafter, the glass tube 130 may be preliminarily drawn to the cane 140 (see FIG. 3B) and arranged into the laminated member 150 (see FIG. 3C) by the method described in detail below. This exemplary embodiment demonstrates the flexibility in manufacturing tubes having various geometrically specific shapes for use in the present invention, which is an advantage in both manufacturability and fiber properties. Connected.

  Referring again to FIG. 1 and FIGS. 2A-2C, in one embodiment, the process can begin with extrusion of high temperature glass into a mold 20. Prior to extrusion, the glass material may be melted at a temperature around 1500 ° C. After the glass is cooled at room temperature, it is reheated to around 700 ° C. to 900 ° C. to enable extrusion. The heated glass is pressed through the mold 20 at a pressure of about 110 kPa to 1.45 MPa (16 to 210 psi) against a 4 inch diameter boule. The extruded tube 30 (shown in schematic top view) has a shape that matches the mold 20.

Depending on the glass material used, additional treatment can be applied to the tube 30 at this stage or at a later stage. For example, when using the above precursor glass, the glass may be subjected to heat treatment after extrusion. You may perform the heat processing of precursor glass at around 580 degreeC. During the heat treatment, phase separation of boron / alkali group (which includes a large amount of alkali and boron oxide) and silica / oxygen group (which includes a large amount of silica) occurs in the glass. The glass material subjected to the heat treatment can be subjected to an elution step for removing the alkali borate thereafter. This elution step can be performed in multiple steps using HNO ₃ (ie, 45 hours or more for 1 mm thick samples and up to 30 days for large 6 mm thick samples). In order to break down the porosity and make a stronger substance (for example, a glass structure formed of densified glass), the glass structure is strengthened by setting the temperature to 1225 ° C. for at least 30 minutes after the elution step 60. Become.

  It has been found that the heat treatment described herein (eg, treatment associated with extrusion) does not interfere with the glass phase separation described above. Accordingly, many of the glass precursor treatment methods of the present invention are feasible. For example, rather than extruding and then heat treating, in another embodiment, the glass precursor may be first heat treated and then extruded. It is believed that the phase separation is not hindered by performing extrusion molding following the heat treated glass precursor described herein. Similarly, in yet another embodiment, the glass precursor may be heat treated so that phase separation begins during the extrusion process, which unifies the two steps.

Glass having a phase-separated network structure around 1-6 nm interconnected by these steps applied to the glass precursors described above (eg, precursors of R ₂ O—B ₂ O ₃ —SiO ₂ ) A structure is formed. As a result of the aforementioned steps, the softening temperature increases from around 670 ° C. (glass precursor) to 1500 ° C. (glass substrate). Furthermore, the glass structure at this stage is porous (volume ratio 28-30%) and has pores with a size of about 1 nm to about 12 nm and an average of about 5 nm to 6 nm. In addition, the glass structure contains at least 90% to about 96% silica by weight (usually 96% silica after elution due to the presence of 4% residual boron in the glass structure). Such a glass structure has high UV transparency, low thermal expansibility, and high softening temperature. For example, when such glass is tempered, it has a transparency in the range of about 80% / mm to about 100% / mm at about 230 nm to 350 nm. Of course, as described above, the treatment may or may not include any number of steps depending on the silica glass used.

  Referring to FIGS. 2A-2C, after formation and potential processing, tube 30 can be predrawn to cane 40 (eg, between draw ratios 2: 1 to 100: 1). In one embodiment, tube 30 has a diameter of about 3 inches (about 7.5 cm) and a length of about 4 feet (about 120 cm). However, various diameters and lengths are contemplated and may depend on the draw ratio for the desired cane 40. For example, cane is generally drawn between 1 mm and 20 mm. The more channels present in the tube structure, it may affect how small the cane should be pre-drawn. Of course, as the cane increases, the number of canes required to form the laminated member decreases (described in detail later).

  With continued reference to FIGS. 2A-2C, once the cane 40 has been pre-drawn and cut, the canes are arranged in an array, ie, in the laminated member 50. This laminated member 50 is then placed in the outer cladding tube 60 to form the preform structure 62. As shown in the figure, 54 canes are arranged in the laminated member 50, and an array of 1996 holes (54 canes × 37 channels / cane) is manufactured. In order to achieve the same number of channels, the prior art would have required stacking at least 3 to 6 times as many capillaries, and in some applications, 1996 capillaries. This ability to produce a large number of larger structures reduces the total number of canes required for assembly and lamination, thus reducing the need for preforms and ultimately fibers as described herein. Consistency is reduced. Furthermore, since a larger tube is disposed in the laminated member, the time required for the process is shortened and the efficiency is increased.

  In addition, since the adjacent canes exactly match each other due to the hexagonal (non-circular) shape of each cane, the canes can be laminated and integrated without providing an unnecessary gap between the canes. The spatial periodicity of the channels in the laminated member 50 is basically the same as in individual canes. Also, an important factor in forming a fiber preform is consistency and straightness through the length of the preform. In contrast to conventional lamination processes, which often have misalignments and gaps, the process described here allows for the simple arrangement of tubes within a laminated member and within a clad tube. By using a larger and stronger cane shaped to match, the possibility of misalignment is further reduced. As a result, the fiber preforms produced by the process described herein are more consistently aligned and straightened through the length of the fiber preform. Arranging the tubes concisely as described herein eliminates the need to examine all cane and fiber lengths to verify that the hole array is in the correct shape, increasing process efficiency.

  In addition, the array formed by the process described herein facilitates the ability to draw fibers with controllable air fill and fine inter-hole pitch. In particular, it is possible to place a large number of channels at any location within the cane (with a more controllable size) through extrusion and to minimize gaps between the canes by closely matching the canes Therefore, the air filling rate and the fine pitch in the photonic crystal fiber can be clearly confirmed and can be manufactured accordingly. The ability to control and / or predict the desired air fill rate and fine pitch can also significantly reduce the amount of etching typically required in conventional processes.

  4A-4B, another embodiment of a tube, a pre-drawn cane, and a laminated member is illustrated. For example, referring to FIG. 4A, the tube 230 has been extruded to have a serrated outer periphery 232 by the process described herein. The tube 230 of FIG. 4A has a serrated outer periphery, but the overall cross-section / perimeter / outer diameter again has a hexagonal shape since tracing the outermost point of the outer periphery will result in a hexagon. Can be regarded as being made. When the tubes 230 as shown in FIG. 4A are pre-drawn 240 and laminated 250, the serrated ends of the tubes fit closely together like a puzzle. If the tube 230 is designed in this way, the surface area between each tube (and finally all the laminated members) can be greatly reduced. Similarly, 4B illustrates yet another embodiment of a tube 330 that has been extruded to have a plurality of semicircles 332 on its outer periphery by the process described herein. Again, since tracing the outermost point of the outer periphery will result in a hexagon, the entire outer periphery, i.e. the outer diameter, can still be considered to have a hexagonal shape. When the tube 330 of FIG. 4B is pre-drawn 340 and laminated 350, the semi-circles fit together to form additional channels between the canes, reducing the surface area. As shown in FIGS. 2-4, many of the embodiments of tubes and laminates (and ultimately photonic crystal fibers) can be manufactured through the processes described herein.

  Referring again to FIGS. 2A-2C, the laminated member 50 is formed with a central channel 56 or gap. Other laminated member embodiments may not have a central channel 56, ie other intentional holes or central channels (eg, laminated members 150, 250 and FIGS. 3A-3C and FIGS. 4A-4B). 350), the central channel of FIGS. 2A-2C creates intentional defects due to light propagation. Due to the flexibility in extruding the tube, any holes or defects within the tube 30 or within the laminated member 50 (by removing the tube as illustrated in FIGS. 2A-2C) are intended. It will be appreciated that can be generated automatically. Further, as shown in FIGS. 2A-2C and as described above, the central channel 56 may be designed with any geometry that is believed to enhance performance, particularly for fibers having the desired bandgap. Can do.

  If desired, the cane 40 of the laminated member may be fused before inserting the laminated member 50 into the clad tube 60 (unbundled tubes are placed in the clad tube and later preliminarily drawn on the structure). As opposed to fusing in). In this step, in order to maintain the alignment of the canes, the canes can be stacked in the array using a hardly soluble jig. The jig can be two square outer pieces and a hexagonal inner piece with a slight gap between the edges to apply a slight pressure on the cane. This jig and cane can be installed in a heating furnace and heated to a temperature at which the cane is fused without deforming the shape of the cane. If desired, pressure can be applied to the cane by placing a weight on the jig and / or widening the gap between the two jig pieces.

As described above with respect to FIGS. 2A-2C, once the cane has been predrawn and cut, the cane may be arranged in a microstructured array, ie, a laminated member. This laminated member is then placed inside the outer cladding tube to form a preform structure. In one embodiment, the volume of the sleeve or tube (eg, the volume of free space directly inside the sleeve defined by the inner surface of the sleeve and the cross-section of the sleeve end perpendicular to the central axis of the sleeve). Kane occupies at least 90%. Further, in one embodiment, the canes can be stacked such that an arbitrary empty space between all the canes excluding the empty central channel is at most 10% of the total volume of the stacked members. The preform may then be pre-drawn 70 into a second cane 80 and covered with another tube 80 for drawing into the fiber. If desired, the preform structure can be drawn directly into a photonic crystal fiber. As a result of the process described herein, more fiber can be drawn from the preform if a larger cane is used in generating the fiber preform. This capability increases fiber production.

  Referring to FIGS. 5A-5C, another embodiment is illustrated in which a laminated member is placed in a glass tube before a cladding tube. In this step, the tube can be extruded and further pre-drawn into the cane 440 as described above (note that the cane 440 shown in FIGS. 5A-5C includes one hole and a hexagonal outline. ). Cover tube 443 may then be extruded to have an inner diameter 444 formed to receive a desired number of molded canes 440. The cover tube can be made of a glass material or any other material, like the laminated member 50. The cover tube 443 may then be cut into first and second members 445 and 446 and subjected to a polishing process. The cane 440 may be laminated within the cover tube 446. Due to the shape of the inner diameter 444 of the cane 440 and the cover tube 443, the cane 440 can be accurately stored in the cover tube 446. Once the cane is laminated, the first member 445 can be coupled with the second member 446 to form the cover tube coupling 447 and then disposed within the cladding tube 460. This structure may be preliminarily drawn to the cane 470 to form the fiber preform 490 and then drawn to the photonic crystal fiber 500.

  Of course, the photonic crystal fiber and the method of manufacturing the same according to the present invention are not limited to the above-described embodiments. Many alternatives, modifications and variations will be apparent to those skilled in the art of the above teachings. For example, a glass material according to the present invention may contain many glasses and precursors useful for making many structures, and use various extruded tubes to assemble fiber preforms. Can do. Thus, although several alternative embodiments have been specifically described, other embodiments will be apparent, that is, relatively easily developed by those of ordinary skill in the art.

20 Mold 24 Pin 30, 130, 230, 330 Tube 34 Channel 40, 140, 440, 470 Cane 50, 150, 250, 350 Laminated member 60, 460 Clad tube 62 Preform structure 490 Fiber preform 500 Photonic crystal fiber

Claims (10)

A method of manufacturing a photonic crystal fiber comprising:
Thermoforming a glass material into a glass tube having a non-circular outer cross section;
Drawing the glass tube to obtain a plurality of canes;
Laminating the cane to produce a preform structure; and
Drawing the preform structure to obtain a photonic crystal fiber;
A method of manufacturing a photonic crystal fiber comprising:   The step of drawing the preform structure includes a step of drawing the preform structure to obtain a fiber preform, and a step of drawing the fiber preform to obtain a photonic crystal fiber. The method of claim 1.   The method according to claim 1, wherein the step of thermoforming comprises extruding the glass material through a mold.   The method of claim 1, wherein the glass tube comprises a plurality of channels extending along an axis of the tube.   5. The method of claim 4, wherein the glass tube comprises at least 19 channels that are essentially parallel to each other and extend along the axis of the tube.   The method of claim 1, wherein the step of stacking the canes to create a preform structure further comprises aligning the canes to generate a preform structure including an empty central channel near the center. the method of.   The method of claim 1, wherein the step of thermoforming the glass material into a glass tube having a non-circular outer cross-section includes extruding the glass material into a hexagonal tube. A method of manufacturing a photonic crystal fiber comprising:
Expressed in terms of weight percent on the oxide basis, _SiO 2 55% to 75%, 5% to 10% of _Na 2 O, 20% to 35% _B 2 _{O 3,} and from 0% to 5% of _Al 2 O Extruding a precursor glass material having a composition consisting essentially of ₃ to obtain a glass tube, the glass tube having a plurality of channels extending along the axis of the tube;
Eluting the glass tube to obtain a porous glass tube containing at least 90% silica by weight;
Heating the porous glass tube so as to collapse holes in the glass tube to form a densified glass, and obtaining a densified glass tube;
Drawing the densified glass tube to obtain a plurality of canes;
Forming a laminated member of the cane, each of the canes being in direct contact with an adjacent cane in the laminated member; and
Drawing the laminated member to obtain a photonic crystal fiber;
A method for producing a photonic crystal fiber, comprising:   The method of claim 8, wherein the tube comprises at least 19 channels extending along an axis of the tube.   A photonic crystal fiber preform structure comprising a plurality of extruded non-circular canes, each of the extruded non-circular canes comprising at least one channel extending along the axis of the cane A photonic crystal fiber preform structure characterized by comprising:

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